1. Field of the invention
The present invention is directed towards a novel shock absorber to be used in automobiles, trucks and similar devices. More particularly, the present invention relates to such shock absorbers employing electro-viscous and electro-rheological fluids.
2. Description of the Prior Art
Conventional shock absorbers are either of a single or double cylinder type. Single cylinder type absorbers have a cylindrical casing filled with fluid (e.g. pressurized gas or oil), and a reciprocating piston that travels within the casing in response to the movement of the struts used to suspend a chassis of an automobile.
Fluid pressure within the cylinder exerts a force opposing the piston travel, thus damping the movement and oscillation of the struts. In a single piston shock absorber, a rod supports the piston within the shock absorber casing and is attached to one of the ends of the strut. As the strut is compressed, the rod is thrust inside the casing, causing the piston and a section of the rod to travel longitudinally. The section of the rod that is thrust within the casing displaces a volume of compression fluid which must be compensated for in order for the shock absorber to function properly. As is known, the displacement of volume in the cylinder often results in mixing of liquid and gas, which can cause fluid foaming that impairs the damping action of the absorber.
Double cylinder type absorbers utilize telescoping outer and inner cylinders. A piston associated with the inner cylinder travels inside an oil filled casing in response to the movement and vibrations of a vehicle. When the piston travels downward, it compresses the oil, forcing it through a valve that is located at the lower end of the inner cylinder and controlling the passage of fluid between inner and outer cylinders. When the piston travels upward, corresponding to decompression of the strut, it forces the oil into the outer cylinder through a second valve located at the upper end of the inner cylinder and controlling a second passage between inner and outer cylinders. When the strut is thrust downward, only a slight damping is needed in order to preserve the spring action of the strut. Considerably larger damping action is required when the strut is extended. For that reason the orifice of the valve located in the lower end of the shock absorber is larger than the orifice in the upper valve.
It has been recognized for several decades that certain fluids respond to the influence of an electric potential by evidencing a rapid and pronounced increase in viscosity and an increased resistance to shear. Such electro-rheological or electro-viscous fluids comprise slurries of finely divided hydrophilic solids in hydrophobic liquids. In the absence of an electric field, these fluids behave in a Newtonian fashion, but when an electric field is applied, the fluids become proportionately more viscous as the potential of the electric field increases. In strong electric fields, the fluids can thicken into a solid. The electro-rheological phenomenon reverses when the electric potential is removed, and the material returns to its fluid state. Electro-rheological fluids change their state very rapidly when electric fields are applied or released, with typical response times being on the order of one millisecond. The ability of electro-rheological fluids to respond rapidly to electrical signals makes them well suited as elements in mechanical devices. Patents directed to compositions of electro-rheological fluids include U.S. Pat. Nos. 3,367,872, 3,047,507, and 4,033,892. Electro-rheological fluids have been extensively used in clutches as disclosed, for example, in U.S. Pat. Nos. 4,444,298 and 4,493,615.
Preliminary efforts directed toward using electro-rheological fluids in shock absorbers or other damping devices produced results that were costly because they required large quantities of the fluids and large electrified sleeves. An improved and less expensive design is disclosed in applicant's co-pending patent application, now issued as U.S. Pat. No. 5,014,829. That shock absorber utilizes a double cylinder design. In one disclosed embodiment, the shock absorber's inner cylindrical casing is filled with electro-rheological fluid and a perforated plunger travels up and down within the casing corresponding to the movement of a strut. The plunger incorporates electrodes positioned so that on activation of an electrical field within the plunger, electro-rheological liquid within the plunger's perforations will solidify. When the plunger moves downward, responding to strut compression, electro-rheological fluid can flow freely through the perforations. When the plunger moves upwards, responding to strut extension, an electronic control system energizes the electrodes within the plunger, solidifying the liquid within its perforations and creating a damping effect. That damping effect can be varied by adjusting timing, intensity and duration of the activation signal.
Another disclosed embodiment in the parent application utilizes a double cylinder oil filled shock absorber in which the flow of oil is controlled by an electro-rheological valve. The valve can be located either within the perforated plunger or in the passageway between the inner and outer casings of the shock absorber. The valve actuator is filled with electro-rheological fluid and contains a perforated piston incorporating one or more sets of electrodes. When the electrodes are energized, the fluid within the piston perforations becomes solid and the valve is positioned to block the flow of oil either through the perforations of the plunger, or through the passageway between inner and outer casings of the shock absorber.
Even though superior to prior designs of the electro-rheological shock absorbers, further improvement is believed possible to the invention disclosed in the parent application. In the parent application the size of the perforated plunger or of an interior electro-rheological valve tends to be limited by the overall size of the shock absorber. Since both the plunger and the valve have a relatively sophisticated internal structure consisting of electrode arrangements, elimination or relaxation of the limitations on size would reduce the overall cost of the device. Further, perforations in the plunger or valve orifices are necessarily small, and the flow of fluid through those perforations or valve orifices may become obstructed, creating some damping action even when the electrodes within the plunger or the valve actuator are not energized. Therefore, the range of the damping effect is limited by that initial damping experienced in the absence of electric field, and that unfavorably affects overall device controllability. Finally, the embodiment employing electro-rheological fluid as the compression fluid is believed to be prohibitively expensive given the present cost of such fluid.
In view of the above, it is a primary object of the present invention to provide a novel shock absorber with an electro-rheological flow control device that is not subject to stringent size limitations inherent in existing designs.
It is a further object of this invention to reduce the cost of manufacturing an electro-rheological shock absorber by relaxing the size limitations on the flow control device.
It is another object of this invention to provide an electro-rheological shock absorber that can be controlled with greater precision than previous devices by increasing the range and the magnitude of its damping effect and through a device configuration that makes flow control action more responsive to the changes in intensity of the controlling electric field.
It is still another object of this invention to provide an electro-rheological shock absorber of a single cylinder type which eliminates fluid foaming effects by compensating for volume displacement created during the downward travel of the plunger within the absorber's casing.
It is a still further object of this invention to provide an electro-rheological shock absorber which compensates for volumetric change in a manner alternative to a floating piston.
It is yet another object of this invention to provide an electro-rheological shock absorber that can be filled with a conventional compression fluid to reduce its cost.
It is a further object of the present invention to provide a shock absorber which is more stable than existing designs and less prone to misalignment and premature wear.